Flexible hang-off arrangement for a catenary riser

ABSTRACT

Flexible hang-off arrangement is provided for a catenary riser suspended from an offshore or inshore platform, which includes floating or fixed platforms, vessels or/and buoys. The bending loads in the top segments of the said riser are reduced by incorporating a pivot at the riser hang-off. Pressure containing welded, bolted, rolled or swaged pipe spools transfer fluids, including hydrocarbons between the riser and the platform. Along significant spool lengths the tangents to the center lines of said spools are orthogonal to and offset from the tangent to the center line of the riser at the hang-off. The said pressure containing spools include arbitrary looped, spiral and helicoidal designs that are subject to torsion.

CROSS-REFERENCE TO RELATED APPLICATIONS

None

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to offshore structures and the risers used toconnect such structures to undersea wells, pipelines and the like. Moreparticularly, it relates to catenary risers, including steel catenaryrisers (SCR's) and catenary risers constructed from other materials liketitanium, and the apparatus used to attach a catenary riser to andsupport a catenary riser from a floating (or fixed) offshore structure.

2. Description of the Related Art Including Information Disclosed Under37 CFR 1.97 and 1.98

DETAILED DESCRIPTION OF THE INVENTION

The top end of a riser, including a catenary riser and including a SteelCatenary Riser (SCR), is typically suspended from a platform (floater,vessel, platform, including a Tension Leg Platform—TLP, spar, buoy, etc)or a platform supported on the seabed (jacket platform, compliant toweretc.). All types of floating structures are referred to herein asfloaters. For example, FIG. 1 depicts an SCR suspended from a truss sparfloater.

Floaters move about their mean design positions (surge, sway and heave)as well as change their angular orientation with regard to their meanposition (pitch, roll and yaw). FIG. 1 b illustrates an example of thecombined surge and pitch or sway and roll motions of a floater have onthe geometry of a catenary riser, which in particular can be an SCR.

The floater motions outlined above are the result of static, dynamic,aerodynamic and hydrodynamic interactions between the floater on itsmooring, currents, wind and waves. What is of particular interest hereare those interactions that result in large translational and angularoffsets of the floater from its mean design positions, like those theexample of which is shown in FIG. 1. Those large offsets have typicallystatic and dynamic components. Static offsets are caused by meancurrents and winds, while large time variable offsets are caused bydynamic interactions of the floater on its mooring with low frequencywave drift forces and with wind gusts. The low frequency floater motionsoccur typically with periods of the order of hundreds of seconds. Thelargest amplitudes of those motions occur where resonance takes placebetween the fluid dynamic forcing, like wave drift forces or/and windgust forces, and the vessel mooring. The vessel moored can typically beapproximated in each of the 6 degrees of freedom as a damped mass-springsystem, whereas the motions for individual degrees of freedom can befairly independent, or static and/or dynamic couplings can exist betweendegrees of freedom. These static and dynamic couplings are representedby the existence of non-zero off-diagonal terms in the stiffness andmass matrices of the dynamic system, respectively.

In addition to mean and low frequency motions floaters are also subjectto so called first order dynamic motions caused by the floater responsesto waves. These motions occur at the wave frequencies, i.e. with periodsfrom a few to a few dozens seconds. For large offshore floaters themotion amplitudes of the said first order motions tend to be smallerthan the static and dynamic offsets caused by the mean forces and thelow frequency forces.

For simplicity, the floaters are approximated herein as rigid bodies,while the geometries of slender structures such as the risers adjust tothe translational and angular offsets of the floater. Riser changes theangles both statically and dynamically due to movements of the hang-offpoint and due to direct forcing and response of riser to wave andcurrent forces.

In particular, the variation in the relative angle between anyorientation on the floater and that of the axis of the riser at thehang-off is of interest herein. The said relative angular floater/riseroffsets can result in high bending loads (and stresses), while thetranslational and combined translational and angular offsets can resultin high variations in the effective tensions at the riser hang-offs.

In those cases wherein SCR motions and the said relative angular offsetsat the SCR hang-off are not very large, the riser stress variations dueto the changes in the said angular offsets and effective hang-offtensions can sometimes be mitigated by adding stress and/or taperedtransition joints at the SCR hang-off. These can utilize steelmaterials, or for larger offsets and stresses titanium alloys can beused. Titanium alloys tend to have higher allowable strains than mosttypical steel materials used offshore and their Young's Moduli tend tobe lower than those of steels. Both the above characteristics oftitanium alloys are beneficial for tolerating high angular andtranslational floater offsets in comparison with the correspondingcharacteristics of steels.

Materials that are more flexible than steel, like for example FiberReinforced Plastics (FRP), can also be used.

In a conventional suspension of the top of an SCR the bending stressesin the SCR are reduced by using a flexjoint, see for example U.S. Pat.No. 5,269,629 (Langner). The use of flexjoints may be combined with theuse of tapered or stepped stress joint, etc., which for similar offsetstend to be shorter and have smaller diameters than those required whenno flexjoint is used.

A flexjoint comprises flexible (rubbery) elastomeric components that‘absorb’ the angular deflections. By the said ‘absorbing’, it is meantthat most of the bending required occurs by deforming the flexibleelastomeric components of the flexjoint thus reducing the amount ofbending and the said bending stresses in the metal components of the SCRsystem. It is noted that elastomeric components of a flexjoint aresubjected to pressure and surface action of internal components. Bothsaid pressure action and physical and/or chemical surface action maylimit the use of flexjoints in particular due to high pressures, due tothermal, erosive, corrosive, etc. action(s) of internal fluids.

Whenever the said flexjoints and/or said stress joints are used asprimary means of reducing bending loads, the effective tension and thebending moment at the hang-off are transmitted to the structure of thefloater. These loads do not exert much load on the piping above theflexjoint or stress joint.

Another solution of an SCR hang-off is shown in U.S. Pat. No. 6,739,804(Haun), which instead of a flexjoint utilizes a universal joint. Unlikewith a flexjoint or a stress joint, the said angular offsets aretransferred to a pipe spool system above the universal joint. In Haun'sdesign, the spools are provided with piping swivels that allow relativerotations of adjoining segments of the spools, and thus bending andtorsional loads and stresses are reduced to relatively small, residualvalues.

In particular:

Flexjoints are expensive and the maximum SCR pressures are limited; theyalso allow limited angular deflections.

Flexjoints require the elastomeric material to be exposed to risercontents and pressure.

Piping swivels are subject to leaks, have limited pressure ratings andalso may require complicated guiding systems to reduce spool bending onthe piping swivels.

At this time, there is little use of torsional deflection in design forthe purpose of stress relieving in offshore pipeline or riser systems.Rigid subsea jumper pipes and pipe expansion spools sometimesincorporate loops, including square loops; ‘L’ or ‘Z’ shapes in order todeal with thermal expansion of pipelines laid on the seabed. The thermalexpansion load relief is through increasing bending, shear and in someof these designs also torsional flexibility of the jumper. However,these designs typically see little torsion that is typically incidentalto axial and transverse loading of those subsea jumpers that havethree-dimensional (3-D) shapes.

There are some patent references to the use of spiral, helicoidal orcoil designs and/or some pivoting arrangements in offshore engineering,but those designs are not in widespread use and they do not involvecatenary risers. Examples include: U.S. Pat. No. 3,189,098, U.S. Pat.No. 3,461,916, U.S. Pat. No. 3,701,551, U.S. Pat. No. 3,718,183, U.S.Pat. No. 3,913,668, U.S. Pat. No. 4,067,202, U.S. Pat. No. 4,137,948,U.S. Pat. No. 4,279,544, U.S. Pat. No. 4,348,137, U.S. Pat. No.4,456,073, U.S. Pat. No. 4,529,334, and U.S. Pat. No. 7,104,329.

Catenary riser pipes routinely see limited torque loading that isincidental to any combination of 3-D bending, shear and tension load.Torsional stresses in the catenary risers due to the said torques areusually small in comparison with other loads.

The torsional flexibility of axi-symmetrical members is, however,utilized in mechanical engineering. For example, torsion rods have beenused as wheel springs in the suspension of many successful automobilesthroughout the twentieth century until now. These do not need to havelarge dimensions in order to accommodate significant vertical movementof a wheel required that is translated to the torsion of the ‘wheel end’of the rod.

SUMMARY OF THE INVENTION

The suspension of the said top of the riser, including a catenary riser,including a Steel Catenary Riser is by means of a pivoting arrangement.The riser can be suspended from a riser porch, a riser bank, a turret ofa Floating Production Storage and Offloading (FPSO) vessel, FloatingProduction Storage (FPS) vessel, buoy, I-tube, J-tube, hawse pipe,fairlead, chute, etc.

The said pivoting arrangement may utilize a ball joint, a universaljoint, a flexjoint, any plurality of or any combination of shackles,chain links, etc, including a single shackle and a single chain link, abellmouth, a chute, an entry or exit to/from an I-tube or/and a J-tubeor/and a hawse pipe that might or might not incorporate a bellmouth, afairlead, a pulley, any arbitrary line re-directing device, etc. Incases where a flexjoint is used, its design could be simpler than thatshown by Langner. In this design the elastomeric components of theflexjoint would typically be arranged external to the pressurecontaining part of the piping, thus considerably simplifying the design.

The said pivoting arrangement resists the tension in the SCR and it alsoresists any transverse forces on the top of the SCR that is suspendedfrom the pivot. However, the pivoting arrangement allows the top part ofthe SCR to undergo angular deflections relative to the said platform,the said floater, the said jacket, the said compliant tower, etc. SCRsare often referred to herein for brevity, because the SCRs are the mostwidely used rigid catenary risers. However, whenever the words ‘SteelCatenary Riser’ or their abbreviation ‘SCR’ are used herein, any type ofrigid catenary riser is meant. This is because, any other metallic,non-metallic, composite, etc. riser that has higher bending stiffnessthan a flexible riser, can be substituted for an SCR in anyimplementation of this invention.

The said angular deflections include deflections in plane and out ofplane of the SCR. Torsional angular deflections of the SCR at the pivotmay or may not be partly or totally resisted by the pivot (in otherwords torsional deflections of the SCR at its hang-off are immaterial tothe designs of interest herein).

Unlike any of the prior art above, this design comprises pipe componentsthat are typically all fixed to each other by means of welding, usingbolted flanges, connectors, swaging, etc., which can tolerate higherpressures and are often more cost efficient than the said prior artdesigns.

In the designs according to this invention, the spools are arranged ingeometrical figures, whereas the axes of the spools (straight, bent orcurved) are offset from and have tangents that form large angles withthe tangent to the top joint of the SCR at the hang-off. By large anglesin particular right angles and angles close to right angles are meant.The said tangent lines of the spools that are close to being orthogonalto the SCR axis at the hang-off would in general not lie in the sameplanes, but in some cases may lie in the same planes.

The said spools can form continuous segmented lines, can be arranged inloops and/or coils and/or spirals and/or helices, so that the bending ofthe top part of the SCR is transformed mostly to torsion in the spools.However, some residual bending and other than torsional shear load canstill be present in the spool system.

Example implementations of this invention featuring example spiral spoolarrangements are depicted in FIGS. 2 through 10.

The said novel designs utilize relatively low torsional stiffness of apipe that allows high angles of twist without generating high torsionalstresses. The arbitrary level of the in-plane and out-of-planerotational flexibilities of the spool system required are achieved byadjusting the lengths of the spool segments and/or by adjusting thediameters or side lengths of the said loops or/and spirals. The saidin-plane and out-of-plane rotational flexibilities of the spool systemrequired are also adjusted by selecting required number of spoolsegments, loops or turns in the spirals as well as by using spoolgeometries that are featured by spool axes being close to perpendicularto the riser axis at the hang-off. In agreement with the generalizedHooke's Law, the longer the said dimensions and the higher the saidnumbers of coil turns, loop turns and/or spiral turns the more flexibleis the system.

Typically, but not necessarily, any straight or segmented lines may bemerged by bends that would have specified their minimum radii ofcurvature. Typical radii of curvature of bends used in pipelineengineering include three times (3D bends) and five times (5D bends) thenominal diameter of the pipe. However, in some designs different bentradii are used.

In particular, the 5D bends are standard bends for pigable risers andpipelines, accordingly bends of 5D or greater radii would be most likelyutilized in riser spool systems. However, not all riser systems need tobe pigable and any standard or not standard bent radius, could be used,including OD [zero-D], for sharp joints between straight or curved pipesegments.

Finite Element Analysis (FEA) demonstrates that, even with very highpressures in the piping and large maximum deflection angles, the saidnovel system can be designed with a limited number of turns in the coilor even an incomplete 360° loop, in the coil, spiral, helix, etc. Thisalso includes different shapes of the spool system that could havesimilar effective lengths subjected to increased torsion. In suchdesigns the risers could be provided with an optional tapered or steppedstress joints on the riser and/or spool sides of the pivot. These wouldsee only relatively limited bending and acceptable bending stresses.

Increasing the diameter(s) and/or the side length(s) of the segmentedspool line(s) of the loop(s) and/or spiral(s) and/or increasing thenumber of segments and/or loops and/or turns in a spiral makes the spoolsystem more flexible. For the same maximum top SCR deflection angle, agreater flexibility of the spool system decreases both bending stressesin the top segment of the SCR and it also decreases torsional stressesin the spools. Or alternatively, an increased flexibility in the spoolsystem allows a greater variation in the maximum SCR hang-off deflectionangle. The said greater flexibility of the spool system can be utilizedboth to reduce quasi static and dynamic bending stresses in the catenaryriser. In particular, greater rotational flexibility helps to reducethat part of bending stresses (and to increase the corresponding fatiguelife), that would otherwise be transferred to the riser from the movingplatform or vessel.

The designs according to this invention that include pivot points at orclose to the effective center of the loop(s) or spiral(s) result inminimum stresses in the spool system. This is because such geometriesminimize the residual bending and shear loads in the spool system (bothnon-torsional and torsional shear). The optimum pivot locations can bedetermined more accurately for any deflected riser-spool system geometryusing well known structural engineering methods.

Examples of designs featuring the effective pivot locations close to theoptimum locations are shown in FIGS. 2 through 7.

However, other solutions incorporating pivots at other locations arealso feasible, even though they result in higher stresses for the sameriser forces and deflection angles and similar spool system geometry,see for example FIGS. 8 through 10. Such other designs might be moreconvenient because they might allow a better access to the pivot and/orthey allow more freedom in geometrical arrangement of system components.The reasons for geometrical variations could be multiple: simplicity ofthe system, access to other components, ease of installation, ease ofservicing or structural examination, etc.

Optionally, piping swivel(s) in the spools can also be included in thenovel designs.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 a presents a typical catenary riser suspended from a truss sparfloater. An example of effects of the spar offsets on the riser geometryis illustrated in FIG. 1 b.

FIG. 2 depicts pivot-spool arrangements featuring ball joints locatedclose to the centers of progressive spirals. FIG. 2 a features acircular spiral spool and FIG. 2 b features a quadrangular spiral spool.

FIG. 3 depicts pivot-spool arrangements featuring flexjoints locatedclose to the centers of progressive spirals. FIG. 3 a features acircular spiral spool and FIG. 3 b features a quadrangular spiral spool.

FIG. 4 depicts pivot-spool arrangements utilizing hawse pipes as pivotsthat are located close to the centers of progressive spirals. FIG. 4 afeatures a circular spiral spool and FIG. 4 b features a quadrangularspiral spool.

FIG. 5 depicts pivot-spool arrangements utilizing I-tube entries orJ-tube entries as pivots located close to the centers of progressivespirals. FIG. 5 a features a circular spiral spool and FIG. 5 b featuresa quadrangular spiral spool.

FIG. 6 depicts pivot-spool arrangements utilizing bellmouths as pivotslocated close to the centers of planar (flat) spirals. FIG. 6 a featuresa circular spiral spool and FIG. 6 b features a quadrangular spiralspool.

FIG. 7 depicts pivot-spool arrangements utilizing universal joints aspivots located close to the centers of spirals. FIG. 7 a features atriangular spiral spool and FIG. 7 b features a pyramidal spiral spoolwith the pyramid shape narrowing upwards. FIG. 7 c features a pyramidalspiral spool with the pyramid shape narrowing downwards.

FIG. 8 depicts a pivot-spool arrangement utilizing a flexjoint as apivot located above the center of a planar (flat) spiral. The circularspiral spool is supported with a 4 leg beam frame.

FIG. 9 depicts a pivot-spool arrangement featuring progressive spiralsoffset to locations above the pivot. FIG. 9 a features a ball joint anda circular spiral spool and FIG. 9 b features a flexjoint and aquadrangular spiral spool.

FIG. 10 depicts pivot-spool arrangements featuring ball joints as pivotsand progressive spirals offset approximately horizontally with regard tothe locations of the pivots, suspended from turrets of an FPSO or anFSO. FIG. 10 a features a circular spiral spool and FIG. 10 b features atriangular spiral spool.

FIG. 11 depicts example details of an SCR hang-off clamp assembly designsimilar to those utilized in the designs depicted in FIGS. 2 through 10and other example details.

FIG. 11 a depicts an example SCR stress joint-gooseneck arrangement.FIG. 11 a also depicts an exemplary hang-off clamp design utilizing aball joint assembly as a pivoting arrangement.

FIG. 11 b depicts an example of a pivot design utilizing a ball joint.

FIG. 11 c depicts an example of a pivot design utilizing a flexjoint.

FIG. 11 d depicts an example of a clamp hang-off design utilizing anuniversal joint.

FIG. 11 e depicts an example of a clamp hang-off design utilizing ashackle and pad-eye assembly.

FIG. 11 f depicts an example of a assembly incorporating a hang-offclamp, shackles, padeye and chain.

FIG. 11 g depicts an example of a buoyancy clamp used on a pipe spool.

FIG. 11 h depicts an example of a helicoidal strake clamp used on a pipespool to suppress Vortex Induced Vibrations (VIVs).

FIG. 11 i depicts examples of bumper-support clamps which may be used ona pipe spool to suppress VIVs and to support the submerged weight ofparts of the spools.

All the pipe elbow bends depicted for sake of examples in FIGS. 2through 11 are planar 5D bends, including all goosenecks as well as allspiral entry and spiral exit bends. It is, however, noted that those areexamples only and that any bend radii can be used in these designs. Theradii of curvatures of the curvilinear 3-D spirals depicted herein areall greater than 5D, either slightly greater or considerably greater. Itmight be also beneficial to use three dimensional bends in some designs.3-D bends might for example make the spool system more compact, whichmight result in lowering stresses, make it easier to connect to otherspool components by extending the lengths of straight pup-joints betweenthose components, allow easier fitting of flanges or connectors into thesystem, etc.

DETAILED DESCRIPTION OF THE INVENTION

An example of a catenary riser 10l suspended from a truss spar floaterplatform 103 is shown in FIG. 1 a. As the spar surges and pitches, atthe riser hang-off location 105 the riser ‘attempts’ to assume in-plane(IP) orientations characterized by dynamic offset angles ranging betweenin plane angular offsets Δθ1 and Δθ2. The angular offsets Δθ1 and Δθ2are measured from the tangent to the riser axis at the hang-off of thedesign catenary of the said riser pertaining to the mean, designlocation of the platform. The in-plane design hang-off offset angle isangle θo, see FIG. 1 b. FIG. 1 b is a detail view from FIG. 1 a.

In addition to surging and pitching floaters also sway, roll, heave andyaw and risers deflect that result in additional out-of-plane and alsomodifications of the in-plane offset angles in addition to those impliedby the surge and pitch. The out-of-plane offsets and those additionalin-plane offsets would be routine for those skilled in the field andaccordingly are not additionally illustrated herein.

Floater surging and pitching can attain large amplitudes, like thoseshown for example in FIG. 1. Typically the surge and pitch motions(named relative to the ‘in-plane’ design plane of the catenary) occurwith different periods and accordingly, from time to time the maximumangular offsets due to the surge and the maximum angular offsets due topitch coincide, as it is shown on the example depicted in FIGS. 1 a and1 b. The range of offset angles Δθ1 and Δθ2 typically increasesadditionally due to additional deflections of the risers that are causedby quasistatic drag forces on the risers and dynamic forces on risers.These quasistatic and dynamic forces result from current and wave(relative current flow) interactions with the system components. Thesaid drag forces can be increased if VIVs are present.

Simultaneously with the variations in the offset angles, the hang-offlocation on the spar moves both horizontally and vertically in-plane(and also out-of-plane) of the catenary. The riser touch-down point(TDP) moves accordingly from the mean design location 107 towardslocations 109 and 111, which are additionally modified by currents. Withthe motion of the TDP between 109 and 111, the submerged weight of thesuspended part of the riser 101 that is supported at the hang-off variesconsiderably, it is the lowest at the TDP at the near location 109 andit is the greatest with the TDP at location 111.

The quasi-static vertical load of the catenary riser at the hang-off 105is approximately equal to the said submerged weight of the riser. Thequasi-static horizontal tension in the riser varies little along thecatenary. This horizontal tension is the greatest when the TDP islocated at 111, and it is the smallest for the TPD at 109.

The total effective tension at the hang-off is equal to the vector sumof the said vertical and the said horizontal load components at thehang-off.

The said total effective tension at the hang-off provides a stressstiffening effect to the SCR structure at the hang-off location 105,which affects the angular deflections of the riser below the hang-off,together with the bending stiffness of the riser and the riser stressjoint at the hang-off, if present.

In a case wherein no pivot is provided at the hang-off 105, therotational stiffness at the hang-off is the bending stiffness of theriser (or the SCR stress joint) at the hang-off. In such a case, thepipe cannot rotate at the hang-off and the relative in-plane angle isconstant at θo, independent of the in-plane or out-of-plane offsets ofthe platform.

In a case where a pivot is provided at 105, the deflection angle Δθdepends on the bending moment and on the effective in-plane rotationalstiffness at the pivot. The said effective in-plane stiffness at thepivot is the sum of the in-plane rotational stiffness of the pivotarrangement (non-zero and typically non-linear whenever a flexjoint isused) and the in-plane rotational stiffness of the spool system, reducedto the location of the pivot 105. The said effective in-plane rotationalstiffness of the spool system combines the torsional stiffness of thespool system together with the bending and shear stiffnesses of thespool system, all reduced to the pivot location 105. For largedeflections the said rotational in-plane spring stiffness is non-linear,but it can be easily determined for any load condition using FEA.Approximate values can be calculated ‘by hand’ using basic structuralengineering approach. Performing the FEA and/or the said approximatehand calculations is known to those skilled in the field.

Words such as “spiral”, “helix”, “coil”, “helicoids”, etc. as may beused herein to describe various embodiments of the invention should notbe limited to definitions thereof used in other contexts (including,without limitation, mathematical works). Rather, the invention is theclaimed method and apparatus described in this disclosure andillustrated in the representative embodiments shown in the drawingfigures. The novel configuration of the stress-relieving segment of ariser according to the present invention is not necessarily a single,geometric shape but rather may comprise a plurality of shapes, both 3-Dand planar, as demonstrated in the illustrated embodiments.

In particular, any spools of types represented in FIGS. 2 through 10, orany of their parts are regarded herein as coils, spirals or helices. Inaddition to the above figures that might or might not be depicted hereinbut which can be strictly or approximately represented in 2-D or in 3-Dby straight or curvilinear segments resembling letters ‘L’, ‘C’, ‘Z’,‘O’, etc that include line segments that are approximately orthogonal tothe axis of the riser pipe near the hang-off are also regarded herein asspirals and claimed as novel according to this invention.

In particular, pipe spool shapes resembling the said letter ‘L’ areregarded herein as partial, approximately half-loop spiral shapes, pipespool shapes resembling letter ‘C’ are regarded herein as partial,approximately three-quarter spiral shapes, etc. whether or not the sidesof the said partial spiral shapes are curvilinear or straight, whetheror not the corners of the said spiral shapes are sharp, or smoothenedutilizing constant or variable radius bends.

In cases when the base riser pipe and the tubing used for theconstruction of a spool system, like for example those depicted in FIGS.2 through 10, the effective combined rotational stiffness of the systemreduced to the hang-off pivot location 105 is low in comparison with thebending stiffness at the stress joint or of the riser pipe at 105,whichever applies, if treated as a rotational spring stiffness.Accordingly, the SCR pipe (stress joint) is almost free to rotate at thepivot, which means that:

The angular offset (rotation angle) of the spool pipe where attached tothe riser (goosenecks 241 and 243 in FIG. 2 or at the pivot, if there isno gooseneck) is almost the same as that of the riser at the pivot.

There is only limited bending in the riser stress joint, in the SCRtapered (or stepped) transition joint and/or the SCR pipe below thepivot—most of the angular offset Δθ is transferred to the spool system205.

The spool systems 205 and 207 are relatively flexible in rotationreduced to the pivot location when compared to the bending stiffness ofthe SCR/stress joint/transition joint at the riser hang-off 105.

Accordingly, most of the bending required is in the designs according tothis invention ‘absorbed’ structurally by combined torsion, bending andshear deformations in the flexible spool system 205 and/or 207. Because,for the same length, a cylindrical pipe is relatively more flexible intorsion that it is in bending, it is preferable to enhance structurallythe torsional flexibility of the spool system. This is carried out byoptimizing the geometrical configuration of the spools. The saidoptimization is best effected by locating the pivot close to thetorsional center of the spool spiral, see for example FIG. 2.

The said combined rotational flexibility of the spool system reduced tothe pivot location can be increased by means of:

-   -   a.—Increasing the lengths of those spool segments that are        orthogonal to the in-plane riser bending plane; this can be        carried out by increasing the diameter of the spiral and/or        increasing the number of the turns in the spiral.    -   b.—Spirals or helices based on polygonal shapes and other        non-circular shapes work better than circular spirals or        helices. This is because the said polygonal shapes utilize        greater pipe lengths per spiral turn than circular spirals do.        By polygonal shapes for example quadrangular, triangular,        pentagonal, hexagonal, and other polygonal, elliptical, oval,        ‘L’-shaped, etc. shapes are meant, including spiral or        helicoidal shapes. The torsional shape effectiveness improves        even more with increasing transverse dimensions of the shapes        used (say diameters of the said entities) and with decreasing        radii of the bends used, (say XD, etc., 10D, etc. 5D, etc., 3D,        etc., 0D; X being an arbitrary, real non-negative number).    -   c.—Minimizing the bending and non-torsion shear stiffness        ‘pollution’, by locating the pivot close to the optimum        (central) location of the said spiral, helix, etc.    -   d.—Keeping the average pitch of the said spiral, helix, etc.        low, for better said orthogonality.    -   e.—Planar spirals or helices arranged in planes perpendicular to        the axis of the SCR at the pivot location are more effective in        converting bending of the riser pipe to torsional loads in the        spools than progressive spirals are. This is because the said        planar spirals are exactly orthogonal to the riser axis at 105.        On the other hand, for progressive spirals, the said angle        oscillates along the spiral around the said orthogonal        direction.

FIGS. 2 through 10 depict examples of structurally effective spooldesigns according to this invention. The design configurations depictedin the figures are examples only that illustrate the principle of thisinvention. Many other configurations according to this principle arefeasible and there are understood to be included in the subject matterof this invention. In addition to that, it is also understood that mostdesign details and variations depicted in FIGS. 1 through 11, thosefeatures and design alternatives described herein as well as all otherdesign variations and solutions, whether general or specific to anyapplications are also covered by the subject matter of this invention.

All the designs depicted on the said figures feature variousimplementations of spiral shapes, because spirals provide geometricallycompact ways of arranging approximately orthogonal pipe lengths in thevicinity of the said pivot locations. However, it is noted that thespools according to this invention do not need to be arranged inapproximately full loop spiral shapes in order to be structurallyeffective. For example, partial loop shapes like for example L-shapesand C-shapes and other segmented line shapes and their combinations,including combinations that reverse the looping directions (the letters‘S’ and ‘Z’ shapes being just some examples of such reversals) can bealso structurally effective in providing the said torsional flexibilityto spool systems according to this invention.

The said segmented lines can feature any combinations of curvilinearand/or straight segments and the statements about spool effectivenesslisted a few paragraphs above apply to all spiral spool arrangements, inthe broadest possible sense highlighted herein. In cases when the saidsegmented lines feature polygons, these can be either regular orarbitrary irregular polygons, including regular and irregular polygonalspiral shapes.

It is also noted that piping adjacent to the spiral spools alsoparticipates in making the combined spool system more flexible, whileintroducing some level of axial asymmetry in the structural flexibilityof the combined system. The said level of axial asymmetry can becontrolled by orienting the spiral entry and the spiral exit spooljoints at different azimuth angles (i.e. angles measured in the planesorthogonal to the riser axis at the pivot point) and at differentmeridional angles (i.e. angles between the riser axis at the pivot andthe axis of the spool). The said level of axial symmetry can be alsocontrolled by using higher or lower numbers of turns or loops in thespirals and by using spirals featuring the said azimuth angle variationsalong the entire spiral length that are closer or farther from integermultiples of 360°. The combined detailed effects of the said spoolgeometry on the 3-D flexibilities of the system can be assessed usingFEA or by performing approximate structural calculations that arewell-known by those skilled in the field.

It is also noted that other non-polygonal and non-broken line shapes ofspirals are also covered by this invention, even though they might havenot been explicitly mentioned or shown on any of the figures. Theseinclude for example approximately spherical, approximately parabolic,approximately elliptic, and conical spirals, etc. and other more complextwo and three dimensional shapes. In particular conical spirals can beregarded as a not shown generalizations of circular spirals in a similarway pyramidal spirals shown in FIGS. 7 b and 7 c are generalizations ofpolygonal spirals depicted on many figures.

FIG. 2 depicts pivot spool arrangements featuring ball joint assemblies201 and 203 located close to the centers of progressive spirals. FIG. 2a features a circular spiral spool 205 and FIG. 2 b features aquadrangular spiral spool 207.

The axial loads on the risers 209 and 211 are transferred to riserporches 213 and 21 5 that are attached to sides of pontoons 217 and 219.Porches 213 and 215 can be attached to any kind of platform known,however, those featured in FIGS. 2 a and 2 b might be used for exampleon semi submersible vessels, or on TLPs, or on FPSOs. It is clear tothose skilled in the field that instead of porches 213 and 215,continuous or non-continuous riser banks that support more than oneriser each could be used, other support structures like for exampleturret structures of an FPSO, etc., can be used instead of porches shownin FIGS. 2 a and 2 b without any loss of generality of this invention.

The tension in the said risers is transferred to hang-off clampassemblies 221 and 223 that are attached to ball joints 201 and 203.Ball joints 201 and 203 transfer the effective tension in the risers tothe platforms through porches 213 and 215. It is noted that FIGS. 2 aand 2 b depict optional bolt connections between hang-off clampassemblies 221, 223 and ball joints 201, 203, respectively. This type ofconnection depicted is an optional solution that is structurallyfeasible, however, in the particular designs depicted in FIGS. 2 a and 2b, as well as on many other figures herein use of full penetration butt,etc. welds between parts like hang-off clamp assemblies 221, 223 andball joints 201, 203 are preferred for structural reasons.

The above is also relevant to joints between other implementations ofpivots, like for example flexjoints, universal joints, etc. and hang-offclamps, see for example FIG. 10 b that demonstrates a use of animplementation of this invention utilizing receptacle basket 1019.

The preferred implementations of this invention involve the use of thesaid receptacle basket 1019 with example designs like those shown forexample in FIGS. 2 a through 3 b, FIGS. 7 a through 8 and FIG. 10. Inmost of these designs, and in many other designs not shown, the saidreceptacle baskets can be preferably incorporated structurally insideriser porches, riser banks, etc. which is a commonly used designsolution known to those skilled in the field. For design implementationssimilar to those depicted for example in FIGS. 4 a through 6 b, thepreferred use of the said receptacles would involve fitting thereceptacle in a bellmouth, in an exit of a hawse pipe, in an exit of anI-tube, in an exit of J-tube, etc., which again is a common practiceknown to those skilled in the field. In these cases it is a commonpractice to permanently clamp the said receptacle baskets to the saidexits of the I-tube, J-tube, hawse pipe, bellmouth, etc. utilizing boltsor other means like latching, etc.

In the preferred designs involving the use of the said receptaclebaskets, similar to 1019 shown in FIG. 10 b, all the joints betweenparts and components like those depicted for example on FIGS. 2 through11, would preferably be welded above the water surface either onshore oroffshore, just before the subsea installation. Accordingly, the systeminstallation operations would be in these cases similar to theinstallations of conventional riser systems in that the ‘principal’structural subsea connection would involve either:

landing the top, fixed end component of a pivoting arrangement in thereceptacle basket, or

pulling-in and clamping, latching, etc. to a bellmouth, an I-tube, aJ-tube, a hawse pipe, etc. the receptacle basket attached to the top,fixed end component of a pivoting arrangement above the surface.

Both the above described classes of design solutions and offshoreinstallation operations pertaining to these solutions are common andwell-known to those skilled in the field. A small modification to anoffshore installation of a conventional riser system would involve thespiral system in the installation procedure. The said spiral system canbe installed subsea:

preferably, while attached to the said riser system utilizing a spiralsupport frame, or similar, if required;

optionally, separately from the riser system either before or after theriser system is installed.

It is noted, that with many implementations of this invention it mightbe possible to incorporate the pivoting arrangement inside thereceptacle basket. Such solution is a common practice and it is shownfor example by Langner in U.S. Pat. No. 5,269,629 that demonstrates suchan arrangement with a conventional riser flexjoint. Flexjoint like thosedepicted for example in FIG. 11 c and elsewhere herein, can also bearranged inside receptacle baskets. Other pivoting arrangements likeball joints, etc. can be also arranged inside receptacle baskets similarto 1019. With regard to specific solutions involving the use of balljoints, it is noted that either:

a meridionally-split external parts of the ball joint similar to thoseshown in FIGS. 2, 10 b and 11 a and 11 b could have their external shapemodified to fit the receptacle basket; the operations of such balljoints would thus be reversed in that the joint would be effectivelyflipped 180° and the said joint ball would be welded, or otherwiseconnected structurally, to the said riser hang-off clamps utilizing atapered stress joint, etc.;

in such cases it would be preferable to use instead more commonarrangements of ball joints featuring the external parts of the saidball joints split near to the joint ‘equatorial’ plane; sucharrangements may be readily deduced by those skilled in the field on thebasis of the description above.

However, it is understood that in the preferred implementations of thisinvention the pivots should be located near to the centers of thespirals and in many cases there might not be enough room inside a spiralfor the pivoting arrangement assembly, for the receptacle basket and forthe structural support of the receptacle basket. In such cases, thereceptacles may be located above the pivoting arrangements as it isshown for example in FIG. 10 b.

Optionally, when the fixed part of the pivoting arrangement is welded tothe riser porch, riser bank, etc., connectors can be used as principalsubsea joints made during the offshore installation of the systembetween the pivoting arrangement 201, 203 and riser hang-off clamp 221,223, see for example FIGS. 7 a through 7 c and FIG. 10 a. The use of thesaid optional subsea connectors includes in particular utilization ofcollet connectors. The use of subsea connectors in the said applicationsis routine for those skilled in the field and with such a use all theparts between the connector and the platform would preferably be welded,etc. together before the offshore installation of the platform used,including vessels and semi submersibles. It is also noted that manyoff-the-shelf connectors available would be appropriate for the saidapplication. It is also noted, that any of the said off-the-shelfconnectors are designed to contain pressure as well as to carry highstructural loads. For the said applications according to this inventionit is often not necessary for a connector utilized to contain pressure,see for example FIG. 2 a and 2 b, FIG. 3 a and 3 b, FIG. 7, etc.Accordingly, in addition to utilizing an ‘off-the-shelf’ connector, thedesign of such a connector could be customized for the applicationaccording to this invention, which might in particular cases involvedesign simplifications. It is also noted that it is also feasible todesign a custom-made connector for the said applications according tothis invention. Many design variations are feasible for the applicationof connectors according to this invention, which will be readily deducedby those skilled in the field.

Bolted connections like those shown for example in FIG. 2 a through FIG.3 b can also be utilized as optional design solutions.

The top segments of risers 209 and 211 would be usually (but optionally)strengthened with optional stress joints 225 and/or 227 and/or withoptional transition joints 229 and/or 231. Typically, transition jointslike 229 and/or 231 shown incorporate several steps (stepped transitionjoints, example 209) with gradually increasing wall stiffnesses, betweenthose of the SCR pipes used 233 and 235 and those of optional stressjoints 225 and/or 227. Alternatively, transition joints can featurecontinuously increasing wall thickness, like those called taperedtransition joints, see 211, whereas the wall pipe wall thickness usedfeatures continuously increasing wall thicknesses between those of theSCR pipes 233 and 235 used and those of the said optional stress joints225 and/or 227. Design details of the said optional stress joint and ofthe said optional transition joints can be selected in ways that areknown to those skilled in the field. The said selections of the designparameters of the optional stress and transition joints need, however,to be selected in ways that are compatible with the design of the novelspirals 237 and 239 according to this invention.

Generally, the stiffer (smaller and/or less effective) the spirals 237and 239, the more need there is to use the optional stress joints 225and/or 227 and/or the more reasons there is to use transition joints 229and/or 231. Once the decisions of using stress joints 225 and/or 227and/or transition joints 229 and/or 231 are made, the stiffer (smallerand/or less effective) are the spirals 237 and 239, the greater wallthicknesses of the said stress joints and the greater the lengths of thesaid SCR transition joints need to be, and vice versa.

Fluids (including homogenous or/and non-homogenous gases and liquidsthat may carry other phases with their flow) transported inside the SCRsare transferred between the risers and spiral spools 237 and 239 usinggoosenecks 241 and 243. The goosenecks can feature the same pipe wallthickness as that used to construct spiral spools 237 and 239, or it canbe greater in order to decrease bending stresses in the goosenecks. Thespecific design choices will depend on detailed stress and fatigueanalyses of the entire riser-spool systems that are performed in usualways well-known to those skilled in the field.

Spiral entry spool segments 245 and 247 connect the goosenecks with thespirals. Spiral entry spool segments 245 and 247 typically incorporatespiral entry bends 249 and 251 and straight or curvilinear pup joints253 and 255. They can also incorporate optionally flanges or connectors257 and 259.

Spiral exit spool segments 265 and 267 connect the spirals with theplatform piping using optional flanges or optional connectors 281 and283. Spiral exit spool segments 261 and 263 typically incorporate spiralexit bends 265 and 267, straight or curvilinear pup joints 269 and 271and they can also incorporate additional, optional bends and segmentslike for example 273 and 275. They can also incorporate optionallyflanges or connectors 277 and 279. Spiral exit spool systems areconnected to the platform piping 285 and 287. Typically, some optionalbending flexibility may be required in the design of the spiral exitspool systems depending on the requirements of any particular structuralsystem. This optional bending flexibility has been achieved in thedesigns shown in FIG. 2 by using those parts of spiral exit spoolsannotated 265, 267 featuring greater tubing lengths than those used forthe spiral entry spool systems. It is noted that many aspects anddetails of design implementations depicted in FIGS. 2 through 11 areshown considerably simplified for the sake of illustration. Inparticular most connections shown as bolted could be optionally bolted,bolted and welded, bolted and welded and additionally reinforced bymeans of component shape interaction, in particular for thoseconnections that transfer axial forces in the riser hang-off system. Thepreference would be for bolted connections not to carry axial loads inthe system, unless the highest loads are transferred by a combination ofshape and full penetration welded connections. It is also noted,however, that the optional use of bolted connections that carry axialloads is also acceptable in designs according to this invention. A closeparallel in the known art would be a use of highly loaded bolted flangesthat are common in offshore riser and pipeline systems.

Typically, but not necessarily in all cases, the design connectionsfeatured herein would be made up for the life of the equipment inquestion, which means that most connections would typically be designedfor a single assembly before or during the installation. Disassembly ofany system components at the end of their design life or in cases ofunexpected failures could be carried out using other means, includingflame or mechanical cutting, cutting using explosive charges, etc. Thosecomponents that might have failed structurally, etc. or might requirepreventive repairs, etc. might be replaced with new components of thesame or modified design or repaired, whatever is preferred.

Shackles, bolts, connectors etc. could be diver-less [for exampleutilizing Remote Operated Vehicle (ROV) and/or other actuations from thesurface] or/and made up with a help of divers, as required. Typicalsubsea equipment (like for example hydraulically and/or mechanicallyand/or electromagnetically assisted bolt tensioning systems, etc.) couldbe used, if preferred so. It is understood that the only some exampledesign implementations of connections are shown, and/or highlightedherein, and many other implementations that may differ from thosefeatured are also covered by the substance matter of this invention.

For simplicity, anodes etc. and other similar details are not shown inFIGS. 1 through 11. VIV suppression devices like strakes, etc. and/orwave and current shielding devices and/or buoyancy devices, etc. arealso omitted from most drawings for simplicity, it is understood thatthey will be used by the designer whenever and wherever so preferred,with any of the design implementations of to this invention.

The wall stiffnesses of spiral spools 237 and 239, spiral entry spools245 and 247 as well as those of the said spiral exit spool systems areselected using usual design approach and preferably confirmed byutilizing FEA. In order to confirm the design using FEA largedisplacement, non-linear FEAs are required that adequately account forthe elbow flexibilities of all the curved elements, including any 2-Delbows (bends) and 3-D curvatures of spirals like 237, in addition toaccounting for stress-stiffening in the riser.

Depending on the degree of sophistication of the software used, it mayor may not be acceptable to use one-dimensional pipe and elbow elementsin the FEAs. In cases the said one-dimensional elements are used,typically in-plane and out-of-plane elbow flexibilities used wouldrequire calibrations using shell and/or solid elements, as required bythe details of the specific system modeled. These include any possibleeffects of bent torsion on the said flexibilities. Additionalcalibration—validation of the modeling techniques needs to account forany 3-D curvatures of the piping used, like that of spiral spool 237.For spool 237 accounting only for in plane and out of plane elbowflexibility might be insufficient.

The design of the SCR/spool piping systems according to this inventionneeds also to take into account in particular:

The ease of installation considerations including assuring structuralintegrities of all components used at all stages of installation and inservice,

The reliability of all the components used, need for access andinspections,

The servicing requirements,

Passive and active corrosion protection, including the use off corrosionresistant alloys and other materials, in particular nearly homogenousmaterials like for example, ferritic and/or austenitic alloys, includingDuplex alloys, including Super-Duplex alloys, including Inconel alloys,etc.

Thermal insulation (or even heating, if applicable) requirements,

Bearing loads and materials used, like bushing, roller bearings andtheir types,

Lubrication requirements for interacting components, like those of theball joints 201 and 203—these might require a use of for example bronze,teflon, nylon, etc. materials on the ball joint or universal jointcontact surfaces,

VIV analyses and suppression or/and prevention, if required,

Stability of the cross-section shapes deformed under the loads applied,

Effects of the deformations of the tubing on structural flexibilities ofsystem components, including elbow flexibilities,

The buoyancy of the pipe per unit length required in order to limitspool system deformations (if necessary) due to the submerged weight;this is in particular important when very heavy wall pipe is used (highinternal pressures),

Need of sheltering the spool systems from hydrodynamic loads byarranging them inside fully or partly enclosed space utilizing shieldsthat protect system components from hydrodynamic forces in currents andwavers, decreasing drag loads by using fairings, etc., if applicable.

Structural design factors and/or load and resistance factors.

Stress concentration factors.

Kind and formulation of elements, etc. used in structural andhydrodynamic modeling, etc.

The above list is typical for any offshore piping/structural system andit might not be complete for particular systems to be designed. Thespecific kinds of requirements are system and design specific and are ineach specific and particular case known to those skilled in the field.

It is noted, however, that the said spiral spools and their entry andexit spool systems can be subjected to significant torsionaldeformations. Torsional deformations might not be well accounted for inmany pipeline, riser and piping and structural codes used in offshoreengineering.

In particular, many design codes do not include allowances for torsionalstraining of the material while computing allowable combined stresses orallowable equivalent Huber—von Mises—Hencky stresses (HMH). Many widelyused engineering codes use simplified, application specific designformulae that might or might not account for torsional stressing or forpipe cross section stability under complex loading including torsion.Adequate, formulations corresponding might be also unavailable from theFEA for some simple line elements (types: pipe, beam, elbow andsimilar).

Accordingly, with regard to these designs, it is recommended to performadditional stress checks. It is in particular recommended to:

Use all stress components, adequate element formulations and adequate,theoretical values of equivalent HMH stress computations provided byFEAs or by detailed stress analyses from ‘first principles’, in additionto those formulated in design codes,

Use design codes that properly account for all stresses and straincomponents in the material, like for example the ASME Boiler andPressure Vessel Code, Section VIII (Division 1 or/and 2), that use forexample the stress intensity in the design. Stress intensity formulationused should account properly for all the stress components, includingstructural, steady state thermal and transient thermal stresses,wherever and whenever applicable.

Select higher design factors than used commonly for piping systems thatare not subjected to torsional shear straining, if necessary.

It is noted that the above modeling, analyses and design considerationsare well-known to those experts skilled in the field. Expert level helpneeds to be sought, whenever in doubt about any of the items highlightedherein.

The selection of pipe material is important. Depending on the maximumstructural and fatigue loads and sizing of the spiral spools high yieldstrength offshore pipe materials or higher strength steels, like forexample AISI 4130 can be used. Generally, the use of higher strengthmaterials allows the engineer to achieve more compact designs. Wherehigher loads occur, higher strength alloys, like titanium alloys can beused. Alternatively, more flexible materials including other metallicmaterials and non-metallic materials, including FRPs can be used.

The materials used can feature very wide ranges of mechanicalproperties. The most important properties are the bulk shear modulus(and the elastic modulus) together with the bulk yield, ultimate andfatigue strength of homogenic, approximately homogenic (steels, alloys,etc. are regarded as homogenic or approximately homogenic for thepurpose of this specification) or composite material used. The followingcombinations of beneficial properties can be used:

High strength materials (examples include most steels, whereas the shearand elastic moduli are typically high in addition to high strengthproperties)

Low shear and elastic moduli and not very high strength materials(examples include some metal alloys, most thermoplastics and many FRPs)

Low shear moduli and high strength materials (examples include titaniumalloys, some FRPs, like some FRPs utilizing for example carbon fibers,nanotubes, KEVLAR® aramid fibers, etc.).

The latter group of the said materials featuring low shear modulicombined with high strength properties provides the most beneficialstructurally set of mechanical properties for construction of the saidspiral spools. When FRPs are used, beneficial low effective (bulk) shearmoduli can be achieved by suitable spatial arrangements of reinforcingfibers in the material. The shear moduli of the fiber material itselfmay or may not be high. Using suitably engineered FRPs or other pipecross-section of complex design can allow achieving low bulk torsionalstiffness, combined with high hoop stiffness and high axial stiffness intension, which the combination is particularly beneficial.

In particular, the spiral spool pipe designs may include usingmultilayer bonded or/and unbonded pipes, whereas different layers mayhave differing construction and differing purpose including, strength,torsional flexibility, pressure containment, corrosion protection, etc.

FIG. 3 depicts a pivot-spool arrangement featuring flexjoints 301 and303 located close to the centers of progressive spirals. FIG. 3 afeatures a circular spiral spool 305 and FIG. 3 b features aquadrangular spiral spool 307.

Flexjoints 301 and 303 used as pivots in designs according to thisinvention do not contain internal fluid pressure like it is shown forexample in U.S. Pat. No. 5,269,629. Accordingly, unlike the designsshown for example by Langner, flexjoints can be successfully utilized inthe designs according to this invention with no internal pressurelimitations. It is noted that wide variety of flexjoint designs can beused successfully in designs according to this invention and that theycan differ in many details from those illustrated for example only inFIGS. 3 a and 3 b.

In particular, the said flexjoints used in designs according to thisinvention can be more compact, can be designed to be more flexible inbending than conventional SCR flexjoints are and they can allow greatermaximum bending angles.

Construction and design considerations related to those implementationsof this invention that are depicted in FIGS. 3 a and 3 b and those ofwide ranges of similar designs will be readily deduced by those skilledin the field on the basis of the detailed descriptions of designsdepicted in FIGS. 2 a and 2 b and considerations highlighted herein.

FIG. 4 depicts pivot-spool arrangements utilizing hawse pipe entries 401and 403 as pivots that are located close to the centers of progressivespirals 405 and 407. FIG. 4 a features a circular spiral spool 405 andFIG. 4 b features a quadrangular spiral spool 407.

The said spirals depicted in FIGS. 4 a and 4 b feature examples ofplacing the spiral assembly in locations that are sheltered fromhydrodynamic loads, like for example those due to the actions of waves,currents and/or relative motions of the supporting structure through thewater. Any of the coiled pipes arrangements according to this inventionand/or adjacent components featured herein can be shielded fromhydrodynamic loads due to VIV, drag and/or inertia forces, etc. byplacing them in a convenient sheltered, shielded or partly shieldedlocation relative the supporting structure or/and by providing speciallydesigned shields. The detailed arrangements of the said shields woulddepend on the degree of sheltering or shielding required, on theposition of the riser hang-off and the type of the supporting structure.The sheltering of shielding from hydrodynamic action can be applied toany extent preferred together with any implementation of this invention.

For example FIGS. 4 a and 4 b depict keel ends of a floater 409 and 411.The said coils 405 and 407 are sheltered in floater moonpools orspecially arranged shafts 413 and 415. Optional shielding surfaces 417and 419 are depicted in FIGS. 4 a and 4 b. Shielding structures 417 and419 can extend in any direction, if required and can provide shelteringor shielding from any side. In particular, shielding structures cansurround completely any coiled assembly according to this invention. Thesaid shielding structures can be arranged totally inside the outlines ofany supporting structure, totally outside the said outlines or/andpartly inside and partly outside the said outlines. Part of theshielding structure 419 shown in FIG. 4 b is optionally hinged for easeof installation.

Any type of said supporting structure can be utilized for said shieldingand/or sheltering. Supporting structures like 409 and 411 featured inFIGS. 4 a and 4 b could for example represent keel fragments of keelregions of a spar, a TLP, a semi submersible or any other floater. Saidcoiled riser hang-off assembly can be located near to the sides of saidmoonpools or shafts, or they can be located away from those sides(internally or externally with regard to the outline(s) of the saidstructures), if necessary, as governed by of any design requirements,functional requirements, available space requirements or/and any kind orrequirements or preferences whatsoever.

Construction and design considerations related to those implementationsof this invention that are depicted in FIGS. 4 a and 4 b and those ofwide ranges of similar designs will be routine for those skilled in thefield on the basis of the detailed descriptions of designs depicted inFIGS. 2 a and 2 b and considerations highlighted herein.

FIG. 5 depicts a pivot-spool arrangement utilizing J-tube entries orI-tube entries as pivots located close to the centers of progressivespirals. The said J-tube is annotated as 501 and the said I-tube isannotated 503. FIG. 5 a features a circular spiral spool 505 and FIG. 5b features a quadrangular spiral spool 507. The J-tubes or I-tubes canbe utilized for example on a spar platform or on any other type of aplatform, vessel or buoy. It is noted that, similar to FIGS. 4 a and 4b, the examplary implementation of this invention depicted in FIG. 5 bfeatures an optional structure shielding spool 507 from waves andcurrents.

It is also noted that in the example implementations of this inventiondepicted in FIGS. 5 a and 5 b the hang-off clamps 509 and 511 shownfeature components that are welded together utilizing full penetrationwelds. In particular both the half-shells of 509 and 511 as well as thehang-off pad-eye plate attachments featured in the said examples arewelded, rather than bolted together. Bolting and welding, as well asbolting only would also be acceptable in these and any similarimplementations of this invention.

Construction and design considerations related to those implementationsof this invention that are depicted in FIGS. 5 a and 5 b and those ofwide ranges of similar designs will be routine for those skilled in thefield on the basis of the detailed descriptions of designs depicted inFIGS. 2 a and 2 b and considerations highlighted herein.

FIG. 6 depicts a pivot-spool arrangement utilizing bellmouths 601 and603 as a pivots located close to the centers of planar (flat) spirals.FIG. 6 a features a circular spiral spool 605 and FIG. 6 b features aquadrangular spiral spool 607.

As it has already been noted planar spiral spools tend to be morestructurally efficient than designs utilizing progressive spiralgeometries. Accordingly, in addition to spirals featuring more than 360°loops, like those shown in FIGS. 6 a and 6 b, loops featuring smallerloop angles, in particular angles smaller than 360° can be used indesigns according to this invention, depending on the range of limitingdesign ranges of in-plane and out-of-plane angles Δθ (including Δθ1 andΔθ2), spool materials used (including FRP and other complex designs) andaccording to the spool geometry, lateral dimensions included. The saidspool shapes featuring loop angles smaller than 360°, include inparticular ‘C’-shaped, ‘L’-shaped spools, etc. These do not need to bearranged exactly in the planes orthogonal to the SCR axes at or close tothe hang-offs like those represented for example by the bellmouths 601and 603.

Construction and design considerations related to those implementationsof this invention that are depicted in FIGS. 6 a and 6 b and those ofwide ranges of similar designs will be routine for those skilled in thefield on the basis of the detailed descriptions of designs depicted inFIGS. 2 a and 2 b and considerations highlighted herein.

It is also noted that some pivot arrangements that utilize chain,connection links and shackles, like those featured for example in FIGS.4 through 6 and FIGS. 11 e and 11 f need to be designed very carefullyand high design factors or component load resistance (including bending,impact abrasion, corrosion, fatigue, etc. resistance) need to be appliedin the design of those components that are continuously and/orrepeatedly subjected to high structural, fatigue, etc. loads. In designimplementations like those featured for example in FIGS. 4 through 6single links happen to be subjected to such high loadings, which mayinclude both in-plane and out-of-plane bending. In particular in-planebending is a common type of bending of chain link or connection linkmaterial, but a combination of in-plane and out-of plane bending alsocombined with associated shear, including torsional shear is somewhatunusual in engineering and it needs to be accounted for in the design ofsuch systems.

On the other hand design implementations of this invention like thosefeatured for example in FIGS. 4 through 6 and in FIGS. 11 e and 11 f dopresent some simplicity and cost effectiveness advantages, both on theconstruction engineering and on the installation engineering sides. Itis noted, that in addition to the said careful design consideration ofthe said high loads it is recommended to utilize said simple and costeffective design solutions for those SCR systems that tend to be lesshighly loaded (smaller diameter SCRs, SCR systems utilizing higherbuoyancies and/or high degrees of thermal insulation, etc.) Detaileddesign and installation implications and considerations related to thoseand similar designs to these highlighted in this paragraph will beroutine for those skilled in the field.

It is also noted, that for higher loaded designs like those similar tothose featured for example in FIGS. 4 through 6, any kinds of pivotsincluding ball joints, flexjoints, universal joints, etc. can beutilized instead of highly loaded links like those depicted on the saidfigures. The ‘fixed’ parts of the said ball joints, flexjoints,universal joints, etc. can be fitted, latched, clamped, etc. at theexits of the hawse pipes, I-tubes, J-tubes, bellmouths, and/or otherarrangements having similar functional purpose, etc. Receptacle basketsor/and subsea connectors can be utilized for that purpose as well, inparticular collet connectors. During the installations the SCR hang-offassemblies can be pulled to their design locations using chain, wire,coiled tubing, etc. and fixed, clamped or/and latched in place.Following the said fixing, clamping or/and latching of the fixed part ofthe pivoting-hang-off assembly, the chain, wire, coiled tubing, etc.that was required for installation can be detached and removed or eitherthe whole of it or a lower part of it can be retained in place asoptional secondary (back-up) attachment means. The upper parts of thesaid I-tubes, J-tubes etc. can be optionally utilized to containplatform piping pertaining to the riser in question, other risers,umbilicals, etc. Platform piping can also be lead outside said I-tubes,J-tubes, hawse pipes, etc. Design solutions like those described aboveare common in subsea engineering and further details are within theroutine expertise of those skilled in the field.

FIG. 7 depicts a pivot-spool arrangement utilizing universal joints 701,703 and 705 as pivots located close to the centers of spirals. FIG. 7 afeatures a triangular spiral spool 707 and FIG. 7 b features a pyramidalspiral spool 709 with the pyramid shape narrowing upwards. FIG. 7 cfeatures a pyramidal spiral spool 711 with the pyramid shape narrowingdownwards.

Use of triangular spiral spools, rather than other shapes can beadvantageous where for example two riser hang-offs need to be locatedclose to each other. For a comparable torsional flexibility of a spiralspool, a spool similar to 707 can be designed to feature a smallerminimum lateral distance 713 between the center axis of the spring 715and the center of a spool pipe cross section 717 than those that arepossible for circular spools or other than triangular polygonal spoolgeometries.

Also, for those designs, where relatively large maximum lateral extents(radii) of spirals 719 are acceptable, triangular spools can featuregreater tube lengths per spiral turn than those spool designs that arebased on higher side number polygons, like for example quadrangles(including squares, rectangles and trapezoids), pentagons, etc. For thesmallest possible maximum lateral dimensions, like for example 719, thispractical advantage is lost, because the tube lengths of all regularpolygon-based spirals tend to the similar length of a circular spiral asthe maximum spiral radius 719 approaches XD (say 5D), the lengths of thestraight tubular segments tend to zero and the spiral geometryprogressively better approximates a regular helix (i.e. a circularprogressive spiral).

Use of pyramidal spiral designs, like those for example illustrated as709 and/or 711 can be advantageous for example depending on installationconsiderations and/or requirements for improved access to the SCRhang-off assembly or/and to the pivot units like for example 701, 703 or705. Other advantages of the said pyramidal, conical and similar spoolgeometries can include:

Staggering the spool geometry in the lateral direction (due to the slopeof the pyramid or the apex angle of a cone, etc.), so that spiral turnsare less likely to come in contact with each other as the spiral deformsunder loads (angular deflection of the riser or/and submerged weight ofthe spiral),

Optimization of the length and weight of the spiral-spool turns closerto the riser end of the spiral and to the spiral entry spools are moreeffective in ‘absorbing’ the angular deflections of the SCR, than turnslying farther away from the riser (i.e. upstream on an export riser).

FIGS. 7 a through 7 c feature optional examples of use of optionalcollet connectors 721, 723 and 725 used for the principal structuralsubsea joints made offshore during the installations of the examplesystems featured. Connectors can be also optionally used on one or bothends of spiral spools, as well as in any other optional locations, as ithas already been mentioned herein.

Construction and design considerations related to those implementationsof this invention that are depicted in FIGS. 7 a through 7 c and thoseof wide ranges of similar designs will be routine to those skilled inthe field on the basis of the detailed descriptions of designs depictedin FIGS. 2 a and 2 b and considerations highlighted herein.

FIG. 8 depicts a pivot-spool arrangement utilizing a flexjoint 801located above the center of planar (flat) spiral. FIG. 8 features acircular spiral spool 803 supported with a 4 leg beam support frame 805.In the optional example depicted beam support frame 805 is pivoted onthe riser hang-off assembly utilizing universal joint 807.

The optional support (spider) beam structures shown in FIGS. 8 can havemultiple purposes, for example:

Provide sliding structural supports to parts of the spiral in order todecrease self-weight/buoyancy generated stresses due to the submergedweight/positive buoyancy of the spool tube,

Provide sliding structural supports to the spiral at preselectedlocations of the tube in order to modify the eigenfrequencies of thespiral spools 803 as the suspended pipe length span control for VIVcontrol means,

Provide sliding structural supports in order to control the spatialregions occupied by the spools in order to prevent their interferencewith other equipment, etc.

The sliding support frame can be pivoted at location 807, like is thespider frame shown in FIGS. 8. The said frame can be also rigidly orflexibly supported from the stress joint or transition joint of the SCR,it can be rigidly or flexibly supported from the floater (using springs,using elastic bungies, catenary lines, etc.).

Beam spider supports featuring any arbitrary numbers of support legs canbe used. In particular, whenever a pivoted or flexible support is usedit is beneficial to utilize 3-leg spider support frames, because of theadvantages of three-point supports in 3-D. Three-point supports tend tobe effective in relieving self-weight stresses and providing reliable(also self-adjustable, if pivoted) span supports.

FIG. 8 shows for example purposes only a spider frame support 805 thatsupports the spiral spool at selected optional locations, whereas everyother spool turn is supported by spider beams at optional locations. Inthe design shown there is no spool-support beam contact at locationsbetween the optional sliding support locations.

A wide range of solutions for the design of optional fixed or movablespool support structures can be implemented. These can providestructural support to any kind of spiral spools that can feature planaror progressive spirals. Greater than one numbers of spool supportstructures that may be pivoted or fixed can be used to support a singlespiral spool, whenever it is necessary or beneficial.

Construction and design considerations related to implementations ofthis invention that are similar to that depicted in FIGS. 8 will beroutine for those skilled in the field on the basis of the detaileddescriptions of designs depicted in FIGS. 2 a and 2 b and otherconsiderations highlighted herein.

FIG. 9 depicts pivot 901 and 903—spool 905 and 907 arrangementsfeaturing progressive spirals 905 and 907 offset to locations above thesaid pivots. FIG. 9 a features a ball joint 901 and a circular spiralspool 905 and FIG. 9 b features a flexjoint 903 and a quadrangularspiral spool 907. For the sake of example platform piping in FIG. 9 isattached to semi submersible or TLP columns 909 and 911.

A qualification related to design examples depicted in FIGS. 9 a and 9 bis that vertical offsetting of the spool center locations with regard tothe locations of the pivots is that often higher stressing of the spoolsresults, or larger spiral dimensions and/or greater number of spiralloops and/or higher strength materials might be required in designs likethose presented in FIGS. 9 a and 9 b than on better stress-optimizeddesigns. The said qualification might be less relevant, or it might notapply or they not apply in cases where high torsional flexibilitymaterials or high torsional flexibility section constructions are used.

The lateral and/or longitudinal offsets of the spiral spools (withregard to the SCR axis and in particular with regard to the hang-offpivot locations) allow the engineer more flexibility in the equipmentdesign. Selections of offset spool locations can be made for reasons ofease of installation, ease of equipment access, ease of spatialarrangement, including staggering of equipment with regard to otherequipment, etc.

Construction and design considerations related to those implementationsof this invention that are depicted in FIGS. 9 a and 9 b and those ofwide ranges of similar designs will be routine for those skilled in thefield on the basis of the detailed descriptions of designs depicted inFIGS. 2 a and 2 b and considerations highlighted herein.

FIG. 10 depicts a pivot-spool arrangement featuring ball joints 1001 and1003 and progressive spirals 1005 and 1007 offset approximatelyhorizontally with regard to the location of the pivots 1009 and 1011.FIG. 10 a features a circular spiral spool and FIG. 10 b features atriangular spiral spool.

FIG. 10 a depicts the riser hang-off assembly optionally sheltered fromthe action of waves and currents inside turret 1013 of an FPSO or FSOvessel. Riser hang-off clamp 1021 is attached to ball joint 1001utilizing optional collet connector 1017.

FIG. 10 b depicts the riser hang-off assembly including the spirallocated outside turret 1015 of an FPSO or FSO vessel. The said riserhang-off assembly utilizes a tapered receptacle basket 1019, which inthe design implementation featured, is used during the systeminstallation as the ‘principal’ structural offshore subsea connection.By using the word ‘principal’ it is meant that said basket 1019 has, forthe example design shown in FIG. 10 b, a similar role from the systeminstallation point of view, to that of connector 1017 depicted in FIG.10 a. In a case spirals 1005, 1007 needed sheltering from waves andcurrents, optional shielding structures (not shown) would be arrangedaround the said spirals and they would typically be suspended from thesaid turrets.

Similar considerations to those highlighted already with regard todesigns shown for example in FIGS. 9 a and 9 b apply. However, spatialarrangement of equipment inside or close to a turret can be particularlychallenging because of the vicinity of other risers, mooring lines, etc.and/or because of space limitations inside a turret.

Construction and design considerations related to those implementationsof this invention that are depicted in FIGS. 10 a and 10 b and those ofwide ranges of similar designs will be routine for those skilled in thefield on the basis of the detailed descriptions of designs depicted inFIGS. 2 a and 2 b and considerations highlighted herein.

FIG. 11 depicts example details of a design of an SCR hang-off clampassembly 1101 that is similar to those utilized in the designs depictedin FIGS. 2 through 10. Additional design details are also shown in FIG.11.

FIG. 11 a depicts an example SCR stress joint 1103—gooseneck 1105arrangement. FIG. 11 a also depicts an example hang-off clamp design1107 utilizing a ball joint assembly 1109 as a pivoting arrangement.

FIG. 11 b depicts an example pivoting arrangement utilizing a ball jointassembly 1109.

The said ball joint example shown is an example only and details of anyball joint design are immaterial to the matter of this invention. Theexploded assembly design shown features for example a meridionally splitbody 1111, 1113 that is assembled utilizing optional locating pins 1115and 1117. Optional fixed spherical bushing surfaces 1119 and optionaladjustable spherical bushing surfaces 1121 are shown. The assemblies canbe welded or optionally bolted together using cover flanges 1123 and1125 and optional stud bolts 1127 and 1129. The ball joint body and thecover flanges can be provided with optional strengthening ribs 1131,1133 and/or 1135.

The external parts of the said ball joint assembly 1109 can beoptionally shaped to fit a receptacle basket similar to that shown forexample as 1019 in FIG. 10 b. As it has already been noted, the optionalbolted connection such as that depicted in FIG. 11 a between hang-offclamp 1101 and ball joint assembly 1111, 1113 might preferably bereplaced with a bolted and welded connection or it might optionally bereplaced with an optional subsea connector.

The ball assembly 1137 can be attached to riser porch 1139 utilizingoptional centering pins 1141 and 1143, optional bolt or optional studs1145 or it can be preferably landed inside the said receptacle basketthat is structurally incorporated into or attached to the said porch.Optionally, ball assembly 1137 can be welded, or otherwise attachedpermanently, to any riser support structure utilized.

FIG. 11 c depicts an examplary flexjoint assembly 1147 connected to ahang-off clamp. Optional high load bolted flange 1148 is depicted inFIG. 11 c, but for most applications use of full penetration butt weldsinstead of bolts, etc. would be preferable. An optional connector couldbe optionally used instead of direct welding.

It is noted with regard to the flexjoint design depicted in FIG. 11 cthat the transmission of all the loads, including the axial and shearforces, relies on the elastomeric material utilized. This arrangement iscommon with some flexjoint designs (example TLP tendon flexjoints), butSCR flexjoints often incorporate a ball joint in their design, whereasthe load path of the axial and shear loading of the entire unit isthrough the said ball joint. It is understood herein that either of thesaid types of flexjoints can be used as a pivoting arrangement in designimplementations of this invention. Detailed design issues related to thesaid types of flexjoints, including those highlighted herein are knownto those skilled in the field.

FIG. 11 d depicts an example hang-off clamp 1151 design utilizing auniversal joint 1153.

FIG. 11 e depicts an example hang-off clamp 1155 design utilizingshackles 1157 and padeyes 1159 assembly.

FIG. 11 f depicts an example assembly incorporating a hang-off clamp1161, shackle 1163, padeye 1165 and chain 1167.

FIG. 11 g depicts an example of a buoyancy clamp 1171 used on a pipespool 1173.

FIG. 11 h depicts an example of a helicoidal strake clamp 1175 used on apipe spool 1173 to suppress VIVs.

Buoyancy clamps of a variety of designs, like those depicted for thesake of examples in FIGS. 11 g and 11 h, can be used on the equipmentdescribed herein for several reasons, in particular:

To reduce self weight loads on the piping due to the submerged weighttogether with the stresses and deformations corresponding,

To improve locally thermal insulation of the piping,

To increase locally the hydrodynamic diameter of the piping assembly andthus shift the frequencies of the VIV excitations,

To suppress VIVs,

To increase locally the hydrodynamic drag of the piping and to modifythe added mass coefficient in order to modify the hydrodynamic anddynamic characteristics of the system, see PCT Patent ApplicationPCT/US2005/046761 (Wajnikonis) which is hereby incorporated by referencein its entirety.

FIG. 11 i depicts an example of bumper-support clamps 1177 used on apipe spool 1173 to suppress VIVs and to support the submerged weight ofparts of the spools. The details of the shapes of the saidbumper-support clamps 1177 as well as the gaps between clamps 1177,their shapes, their buoyancies and sizes of the said bumper-supportclamps 1177 used need to be optimized in the design process of anyparticular system. Bumper support clamps 1177 that are used in differentlocations on spools 1173 could be of different sizes, as featured as anexample only in FIG. 11 i, or they may be of the same size. In additionto the above bumper-support clamps 1177 may be provided with contactshoes (not shown), which may be used in order to adjust any gaps betweencomponents to values required.

The example of a bumper-support clamp depicted in FIG. 11 i can have anycombination of functional purposes in addition to those listed above.These may include in particular:

Providing discrete or continuous support to the piping in order tomechanically control the deflections of the equipment due to self weightand/or due to hydrodynamic loads in waves and currents,

Providing discrete or continuous support locations to the piping inorder to modify the eigenfrequencies of the system and thus controlVIVs.

The nearly continuous or continuous supports can be achieved by usinglarge numbers of said bumper support clamps installed densely on thepiping.

Depending on the design requirements of a particular system, the saidbumper clamps can be provided with loose or tight optional shapeprotrusions 1179 made of the same or of different materials, looseoptional sling connections 1181 and/or 1183 etc. in order tomechanically tie spiral loops together (1179) and/or in order to moreeffectively anchor the system (1181, 1183) and thus effectively protectthe system from the actions of currents and waves.

The shapes of the bumper clamps as well as the said optional protrusionsand/or optional sling interconnections need to be designed so that thepiping had sufficient capability to undergo torsional deformations asper the objectives of this invention.

It is noted hereby that combinations depicted in Figures utilized hereinare examples only. In particular the combinations of any particularpivoting arrangements shown with those of any particular spiral spoolarrangements shown and with any kind of structure or arrangement thatsuspends the spool/pivoting arrangements on any particular type ofvessel, buoy, turret, etc are examples only and they can be freelyinterchanged without affecting the generality of this invention. Evenmore arrangement combinations can be designed according to thisinvention, which include spiral designs that are not depicted on thesaid figures (like L-shaped spirals, C-shaped spirals, etc.).

Although the invention has been described in detail with reference tocertain preferred embodiments, variations and modifications exist withinthe scope and spirit of the invention as described and defined in thefollowing claims.

1. Riser-deflection spool assembly, whereas: said riser, including acatenary riser is suspended using a pivoting arrangement from anoffshore platform, including fixed platform, including an articulatedplatform, including a compliant platform, including a floating platform,including a floating vessel, including a floating buoy, said pivotingarrangement transfers tension in said riser to the structure of saidplatform, including a core of a turret structure that might useapproximately fixed orientation with regard to the geographicaldirections, while said platform utilizing said turret might be allowedto rotate freely around said core of said turret, said pivotingarrangement allowing means to transfer directly to said platform,including said turret of said floater relatively small fractions ofbending moments applied to said riser at the said pivoted points of saidriser suspension, said riser being also connected to said platformrelatively flexibly using pressure containing piping spools, saidpressure containing piping spools being arranged spatially in mannersthat expose a significant percentage of the total length of saidpressure containing piping spools to torsional deformations resultingfrom any combination of in-plane and out-of-plane bending of said riserrelative to said structure at the location of said pivoting arrangement,said combinations of in-plane and out-of-plane bending resulting incorresponding combinations of relatively free in-plane angulardeflections and out-of-plane angular deflections of the axis of saidriser at said location of said pivoting arrangement, said pressurecontaining piping spools comprising components connected by reliablepressure containing means, including welding, including bolted flanges,including subsea connectors and including plastically deformed durablyrolled connections, including cold rolled connections and includingswaged connection, said pressure containing piping spools includingspools involving coiled shapes of spools, including circular spiralshapes and including polygonal spiral shapes.
 2. Said pivotingarrangements according to claim 1 including ball joints, includingflexjoints, including universal joints, including bellmouths, includinghawse pipes, including chutes, including I-tubes, including J-tubes,including fairleads, including pulleys, including any combinations ofshackles and chain links, connecting links and pad-eyes.
 3. Said riser,said pressure containing piping, including said deflection spoolassembly and said platform piping according to claim 1 incorporating andbeing interconnected utilizing piping elements featuring minimum radiiof curvature of pre-determined minimum values, including those ofpredetermined ratios of bent radii to the nominal pipe diameters,including those of five times nominal piping diameters.
 4. Said pressurecontaining piping, including said deflection spool assembly beingsubject to torsional deformations according to claim 1 being constructedof steel alloys used in riser and pipeline engineering, including highstrength alloys, including corrosion resistant alloys including othersteel alloys.
 5. Said pressure containing piping, including saiddeflection spool assembly being subject to torsional deformationsaccording to claim 1, utilizing corrosion resistant materials, includingalloys, including being constructed of corrosion resistant materials,and including utilizing corrosion resistant materials for internalcladding, and including utilizing corrosion resistant materials forinternal plating, etc.
 6. Said pressure containing piping, includingsaid deflection spool assembly being subject to torsional deformationsaccording to claim 1 being constructed of high strength steel alloys. 7.Said pressure containing piping, including said deflection spoolassembly being subject to torsional deformations according to claim 1being constructed of relatively low shear modulus and high yield andultimate tensile material, including titanium alloys.
 8. Said pressurecontaining piping, including said deflection spool assembly beingsubject to high torsional deformations according to claim 1 beingconstructed so that low torsional stiffness of the pipe cross sectionresults, while the maximum design pressures are reliably contained,which includes utilizing fiber reinforced plastic materials.
 9. Saidpressure containing piping, including said deflection spool assemblyaccording to claim 1 being subject to any combination of high torsionaland high bending deformations being constructed so that a combination oflow torsional stiffness of the pipe and of low bending stiffness of thepipe results, while the maximum design pressures are reliably contained,which includes fiber reinforced plastic materials.
 10. Said pressurecontaining piping, including said deflection spool assembly beingsubject to high torsional deformations according to claim 1 comprisingmore than one layer, including multilayer constructions that mightincorporate cladding, and including multilayer constructions that mightincorporate plating, and including layers that might be swaged together,including any combinations of layers that might be interlocked,including any combinations of layers that might be bonded together andincluding any combinations of layers that might be not bonded.
 11. Saiddeflection spool assembly according to claim 1 featuring riser systemthat is suspended from a platform, including a floating platform and afloating vessel, utilizing shape type interaction to transfer high loadsbetween the components of the system, including a use of receptaclebaskets, and including a use of connectors, which includes a use of asingle connector, in particular collet connectors and a colletconnector.
 12. Said deflection spool assembly according to claim 1utilizing design means of protection against vortex induced vibrations,including devices that shield selected parts of the system from theaction of currents and waves and including vortex suppression devices.13. Said deflection spool assembly according to claim 1 utilizing therotational flexibility of said deflection spool assembly in order toreduce dynamic bending stresses in said catenary riser that result inincreasing fatigue life of said riser.